My good man, are you on Linux ?
Altho, I've not had a need for this workaround since the Deadlock version where they added Christmas "hats".
Nowadays I dont have any compatability or launch option parameters set for Deadlock in steam, thing just works silky smooth at 144FPS.
Perhaps try a full reinstall of the game if you are on Linux.
game launch parameters, try using this:
LD_PRELOAD="" %command%
I dont know the specific moment in time when proton shat the bed, but since proton 8 or 9 dropped, i observed degradation in stability and overall quality of the tool.
Now, after purging mangohud (and that not getting rid of FPS drops), I stumbled upon LD_PRELOAD, whats LD_PRELOAD you ask ? I have absolutely no clue, but a bit of inspiration can be found around the www, the funny part is, many have no clue wth this thing truly does, but only that it helps, lol...